ocular pain and the trigeminal nerve Flashcards
what are the 2 classes of somatic sensory receptor ?
- free nerve endings
. pain or temperature sensitive - specialised mechanoreceptors
. tactile receptors ( touch , pressure )
. proprioceptors ( joint position )
how is the somatic sensory innervation of all the face and eye controlled ?
via trigeminal (5th ) cranial nerve which mediates tactile , thermal and pain sensation .
where are the somatic sensory receptors in the eye ?
. anterior corneal surface/epithelium
. inside the eye ball : uvea = comprises several tissue in the eyeball specifically the choroid , ciliary body and iris
.orbital contents and eyelids + conjunctiva
what is the significance of somatic sensory innervation ?
. it is about ocular defence
when foreign bodies land on surface of your cornea , so the sensory receptors alert you to the presence of those via the corneal eyeblink reflex
-Ocular pain
what is the significance of ocular pain ?
alerts the PX to damage or disease
what are major branches of trigeminal ( 5th ) cranial nerve ?
. ophthalmic ( V1 ) - takes sensory information from anterior corneal epithelium , uvea and upper eyelid and conjunctiva and lacrimal gland
. maxillary ( V2) - branches of maxillary nerve that supply lower eyelid and conjunctiva
. mandibular ( V3) - lower jaw + teeth
what are the 3 main ophthalmic ( v1 ) nerve branches ?
- nasociliary nerve : takes the medial orbital path
. long and short ciliary branches - take sensory information from inside the eye and the surface of the cornea
. nasal branches : take sensory information from inside the nasal cavity
. infra-trochlear :
medial upper eyelid + conjunctiva - lacrimal nerve :takes the lateral orbital path
takes sensory information form the lateral upper eyelid + conjunctiva and lacrimal gland
3.frontal nerve : runs through upper orbital path
takes sensory information from the skin of your forehead and scalp
how the 3 main ophthalmic ( v1 ) nerve branches exit the orbit ?
exit the orbital via superior orbital fissure as V1
what do all small nerves and the 3 main nerve branches contain ?
. peripheral axons of things which are trigeminal ganglion cells
. each nerve branches ophthalmic , maxillary and mandibular have axons whose cell bodies sit in that ganglion and come together to form 5th trigeminal nerve root that goes into the brain stem and sends sensory information to various nuclei within the brain stem
where are the trigeminal ganglion cells located ?
trigeminal ganglion cell bodies sit in a bag just outside your brain stem
what does the surface of cornea contain ?
contains very high density of these different types of sensory receptor
where are the receptors in the cornea and ( uvea ) present ?
. receptors are present in the anterior epithelium
. their axons pass via bowman’s membrane to
- run radially through the stroma to leave in all directions at the limbus and enter the supra-choroid just below the sclera
- and join axons coming from receptors in the uveal tract and those axons also leave via short and long ciliary nerves at back of your eyeball
what are the two types of receptors in the axons in the long and short ciliary nerves leaving the back of the eye ?
. 50% specialized mechanoreceptors which signal touch and pressure
- they produce phasic ( fast - adapting ) responses to mechanical stimulation only
. 50% poly-modal nociceptors from free nerve - endings ( pain )
- they are tonic / long lasting ( slowly adapting ) responses to different noxious mechanical , thermal and chemical stimuli
what does poly-modal mean ?
pain receptors might respond to noxious severe mechanical deformations to cuts or stabs
. respond to severe thermal stimuli
what is a simple mechanism for ocular defence ?
corneal - eyeblink reflex
what are the two types of corneal - eyeblink reflex ?
- sensory limb : light corneal touch/dryness - mediated by 5th trigeminal nerve
. activates receptors on corneal surface
.those receptors have axons travelling via long ciliary , nasociliary and ophthalmic nerves
. then axons travel via 5 th nerve root to trigeminal brainstem nuclei which then signal to nuclei which signal to orbicularis oculi muscle which is blinking muscle - motor limb : close eyelids/blink - mediated by 7th facial nerve
. somatic motor neurons in main facial nucleus
. axons run in facial nerve , then travel via temporal and zygomatic branches to forcefully contract orbicularis oculi
what are the two major parts of the orbicularis oculi muscle ?
palpebral - part that runs through the eyelids themselves
contract during gentle blinking
orbital - runs through the orbital rim
forceful contraction used during ocular defence
what kind of tissue damage do pain stimuli and nociceptors respond to ?
respond to tissue damage caused by combination of :
. mechanical deformation ( pinch , cut )
. temperature extremes ( heat ,cold)
. chemical irritants ( e.g. acid , histamines )
how are pain stimuli detected ?
by 2 major nociceptors
what are the 2 major nociceptors classes ?
- c- fibres : 2/3 of receptors in cornea
. small diameter , unmyelinated axons thus slow rate conduction
. respond to dull , aching , throbbing ( cold ) and stinging pains
. usually polymodal respond to any/all of the 3 types of tissue damage
. activated by this particular chemical capsaicin
. respond to histamine also - A𝛿-fibres : small diameter axons , some myelin
. respond to mechano-thermal receptors , not chemical
. respond to sharp , stabbing , hot pain
what is the difference in pain localisation between skin tissues and visceral seep tissues = eye ?
- cutaneous ( skin ) tissue
able to localise pain accurately in the surface of your skin this is sue to
. free nerve endings in skin that belong to a single axon
. free nerve ending is only responsive to stimuli from a very small region - visceral ( deep ) tissues = eye ?
.many , widespread endings per axon
. large receptive field and overlapping
. poor localisation of noxious stimuli
. can be referred
what does referred pain mean ?
pain perceived at a location that is not the actual injury site
e.g. pain down left arm with heart attack this is because those axons have branches that go to both of those tissues
what are some causes of ocular pain ?
- naturally - occurring or in the eye
. dry eye and corneal scratches ( irritation )
. uveitis ( infection ) , glaucoma ( raised IOP )
. tumors ( e.g. melanoma ) formed by melanocytes - naturally - occuring oustide the eye
. orbital blow out fracture ( trauma )
. conjunctiva and orbital cellulitis ( infection )
. optic neuritis ( inflammation of optic nerve )
. herpes zoster ophthalmicus ( inflammation of V1 ) - latrogenic ( caused by health care professionals )
. eye drops ( e.g. acidic vehicle for atropine )
. laser surgery ( to repair retinal tears )
what is the condition anterior uveitis ?
. inflammation of uveal tract
so iris and ciliary body and choroid will be inflamed
. this causes deep dull pain which caused by the release of histamine
. can also be caused by autoimmune, microbial
. T-cell mediated
. spreads from uvea and gets into blood vessels
. anterior iridial circle also becomes inflamed
. detected by circum - limbal flush
. treated by steriods which causes immune suppression and anti inflammatory